This invention relates to stable liquid biuret modified toluene diisocyanates, prepolymers thereof, stable liquid biuret allophanate modified toluene diisocyanates, prepolymers thereof, and to processes for the preparation of these compositions. The stable liquid biuret modified toluene diisocyanates comprise a secondary amine based biuret modified TDI having an NCO group content of about 16 to about 46% by weight.
Modified isocyanates, including aromatic diisocyanates are known and described in the art. Various modifications include, for example, allophanate modified, biuret modified, carbodiimide modified, isocyanurate modified, uretdione modified, urethane modified, oxadiainetrione modified and various combinations thereof.
Biuret modified diisocyanates including those based on aromatic diisocyanate and prepolymers thereof, are known and described in, for example, U.S. Pat. Nos. 4,618,706, 4,677,136, 4,703,100, 4,837,359, 5,212,275, 5,428,124 and 5,994,491.
More specifically, U.S. Pat. Nos. 4,667,136 and 4,703,100 describe urea and/or biuret group containing polyisocyanates prepared by reacting an organic polyisocyanate and a high molecular weight (500 to 20,000) polyether or polyester containing at least two isocyanate-reactive groups which may be primary and/or secondary hydroxyl and/or amine groups and mixtures thereof), and optionally, a low molecular weight compound comprising one or more of aromatic diamines or triamines, (cyclo)aliphatic diamines of triamines, organic compounds containing at least one hydroxyl group and at least one amine group, organic compounds containing at least two alcoholic hydroxyl groups (and optionally an ether or ester group), and a hydrazine containing at least two reactive NH groups. Processes for the preparation of these urea and/or biuret modified isocyanates are also disclosed.
U.S. Pat. No. 4,837,359 discloses biurets prepared from a (cyclo)aliphatic diisocyanate and a (cyclo)aliphatic primary diamine compound. Biurets based on aromatic diisocyanates and diamines having aromatically attached amino groups and processes for their preparation are described by U.S. Pat. Nos. 4,618,706 and 5,994,491.
Urea and biuret prepolymers of diphenylmethane diisocyanates are known and described in U.S. Pat. Nos. 5,212,275 and 5,428,124. U.S. Pat. No. 5,212,275 describes liquid prepolymers of ureas and/or biurets prepared by reacting a polyfunctional secondary amine group containing compound corresponding to a specific structure with a polyisocyanate of the diphenylmethane series. Storage stable, liquid prepolymers of MDI containing urea and/or biuret groups are disclosed in U.S. Pat. No. 5,428,124. These are prepared by reacting an aminocrotonate with a mixture of MDI having a specified isomer distribution.
Allophanate modified diphenylmethane diisocyanates, prepolymers thereof, etc. are known and described in, for example, U.S. Pat. Nos. 5,310,053 and 5,310,054. The liquid stable products of U.S. Pat. No. 5,319,053 are characterized by an NCO group content of 12 to 32.5%, and comprise the reaction product of an aliphatic alcohol and a specified mixture of isomers of diphenylmethane diisocyanate. This reference also discloses stable liquid MDI prepolymers which comprise the reaction product of the allophanate-modified MDI as described above, with an organic material containing two or more active hydrogen groups. U.S. Pat. No. 5,319,054 describes liquid allophanate modified MDI compositions which are storage stable at 25° C. The diphenylmethane diisocyanate has a specific isomer distribution requiring 2 to 60% by weight of 2,4′-diphenylmethane diisocyanate.
Allophanate modified diphenylmethane diisocyanate prepolymers are described in U.S. Pat. No. 5,440,003. These products are stable liquids at 25° C., and comprise the reaction product of an isomeric mixture of diphenylmethane diisocyanate and an aromatic alcohol such as phenol, with the resultant product being converted to the allophanate having an NCO group content of 12 to 32% by weight.
U.S. Pat. No. 6,271,279 discloses flexible foams prepared from toluene diisocyanate diol allophanates and the process for the preparation of flexible foams from these. These allophanate modified polyisocyanates are liquids and storage stable, and characterized by an NCO group content of about 20 to 42%.
U.S. Pat. Nos. 6,028,158 and 6,063,891 are directed to freeze-stable allophanate modified toluene di- or poly-isocyanate partial trimers; to freeze-stable blends of these allophanate modified toluene di- or polyisocyanate partial trimers with polymethylene poly(phenylisocyanates); to freeze-stable urethane prepolymers of these allophanate modified, partially trimerized toluene di or polyisocyanates; to freeze-stable blends of the urethane prepolymers of the allophanate modified, partially trimerized toluene di- or polyisocyanates with polymethylene poly(phenylisocyanates); and to processes for the preparation of these products.
Another trimer of toluene diisocyanate is disclosed in U.S. Pat. No. 4,456,709. These are also described as being liquid and storage stable at room temperature. The polyisocyanates of the '709 patent are mixtures characterized by an NCO group content of 36.5 to 45% by wt., and consist essentially of (a) 25 to 70 parts by wt. of a mixture having an NCO group content of 22 to 36% by wt. of (i) isocyanurate group containing trimers of 2,4-diisocyanatotoluene and (ii) 2,4-diisocyanateotoluene, and (b) from 30 to 75 parts by wt. of 2,4- and/or 2,6-diisocyanatotoluene.
Advantages of the present invention include stable liquid products having unique structures and higher functionalities than other biuret modified isocyanates, biuret-allophanate modiified isocyanates and prepolymers thereof. Higher functionalities are expected to result in faster cure rates in foams.